Melt 2 squares unsweetened chocolate. Blend 2 teaspoons light Karo syrup, 2 teaspoons vanilla, 2 tablespoons soft margarine, 1/2 cup powdered sugar and 3 tablespoons milk.
Butter a 9x13 pan. Line with one third of the graham crackers. Mix pudding and milk and beat at medium speed for 2 minutes. Blend in Cool Whip. Pour 1/2 mixture over crackers. Put second layer of crackers over mixture. Pour remaining mixture in and cover with another layer of crackers. Refrigerate two hours, then frost.
Refrigerate 24 hours before serving.